Choosing the state structure in code
const visibleTickets = tickets.filter(ticket =>
filter === "all" || ticket.status === filter
);Read the example from data and control flow to the resulting UI. Keep the component boundary small.
Back to week 2
Topic
Choosing the state structure
Definition
Well-structured state stores minimal, non-redundant values in a shape that reflects independent changes.
In simpler words
Keep only the values you cannot calculate from other values, and avoid contradictory copies.
Avoiding redundancy, duplication, and deeply nested state.
After this you can
- Choose state that remains easy to update and reason about.
- Explain the trade-off to a teammate using a small example.
- Name at least one common bug pattern for this topic.
Understand Choosing the state structure
Avoiding redundancy, duplication, and deeply nested state.
Start by identifying which value or browser behavior changes. Then describe the UI from that current input instead of editing the DOM as a separate source of truth.
Apply Choosing the state structure
Keep rendering as a calculation. Put user-triggered changes in event handlers, preserve UI memory in state, and reserve external synchronization for Effects or the server-state layer.
Name values by their UI meaning, test the loading and error path when data is remote, and avoid keeping two editable copies of the same value.
Ask before adding code: is this local UI memory, shared client state, or Nest-owned server state?
Where bugs hide
Definition
High-bug areas are places where a small API misuse looks correct but produces stale UI, duplicate work, or silent failures.
In simpler words
Each mistake below shows Wrong vs Right code — compare them side by side.
When something misbehaves, match the symptom to a pattern below before rewriting the feature.
Prefer fixing the ownership or update path over adding another Effect or sync step.
Mistake: Storing derived filtered list
// Wrong
const [visible, setVisible] = useState([]);
useEffect(() => setVisible(items.filter(...)), [items, filter]);
// Right
const visible = items.filter(...);Derive during render — no sync Effect.
Mistake: Two copies of the same field
// Wrong
const [title, setTitle] = useState("");
const [ticket, setTicket] = useState({ title: "" });
// Right
const [ticket, setTicket] = useState({ title: "" });
// read ticket.titleOne source of truth prevents disagreement.
Mistake: Deep nesting for forms
// Wrong
state.user.profile.settings.theme
// Right
// flatter: theme + profileId, or multiple small statesDeep trees make immutable updates error-prone.
Live playground
Choosing the state structure sandbox
Change one input at a time and predict the next render.
Prefer deriving openCount — mirrored state can drift.
Derived open count: 2
Keep in mind
- Keep the formal definition in mind; it explains which tool belongs where.
- Prefer one source of truth over synchronized copies of the same value.
- When behavior surprises you, trace: input → update → render → committed UI.
- Study the Wrong vs Right examples in “Where bugs hide” before you merge.
Test
Check your understanding
At least 10 questions — mix of concept, syntax, practical, and logic. Score ≥ 80% (enforced by the API) to save progress.
Checking your session…
10 questions · concept 3 · syntax 3 · practical 2 · logic 2